Reducing the actuation voltage of microelectromechanical system switches

ABSTRACT

A microelectromechanical system switch may include a relatively stiff cantilevered beam coupled, on its free end, to a more compliant or flexible extension. A contact may be positioned at the free end of the cantilevered beam. The extension reduces the actuation voltage that is needed and compensates for the relative stiffness of the cantilevered beam in closing the switch. In opening the switch, the stiffness of the cantilevered beam may advantageously enable quicker operation which may be desirable in higher frequency situations.

BACKGROUND

[0001] This invention relates generally to microelectromechanicalsystems (MEMS) and, particularly, to MEMS switches.

[0002] Microelectromechanical switches have intrinsic advantages overtraditional solid state switches, including low insertion loss,excellent isolation, and superior linearity. However, for higherfrequency switching operations, MEMS switches may be too slow or mayrequire too much actuation voltage. This is especially true in radiofrequency transmission or receiving switching applications.

[0003] Because the speed of a mechanical switch is limited by itsresonance frequency, the speed may be increased by increasing thestiffness of the switch. However, a stiff switch requires higheractuation voltage for the switching actuation.

[0004] Thus, there is a need for a way to enable MEMS switches to reactmore quickly without requiring significantly higher actuation voltages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is an enlarged cross-sectional view of one embodiment ofthe present invention;

[0006]FIG. 2A is a cross-sectional view corresponding to FIG. 1 with theswitch in a first position;

[0007]FIG. 2B is a cross-sectional view corresponding to FIG. 1 with theswitch in a second position;

[0008]FIG. 2C is a cross-sectional view corresponding to FIG. 1 with theswitch in a third position;

[0009]FIG. 3A is a cross-sectional view of the switch shown in FIG. 1 ina fourth position;

[0010]FIG. 3B is a cross-sectional view of the switch shown in FIG. 1 ina fifth position;

[0011]FIG. 3C is a cross-sectional view of the switch shown in FIG. 1 ina sixth position;

[0012]FIG. 4 is an enlarged top plan view of the switch shown in FIG. 3Cin one embodiment of the present invention;

[0013]FIG. 5 is an enlarged cross-sectional view of another embodimentof the present invention; and

[0014]FIG. 6 is a top plan view of the embodiment shown in FIG. 5.

DETAILED DESCRIPTION

[0015] Referring to FIG. 1, a microelectromechanical system (MEMS)switch 10 includes a cantilevered beam 16 mounted on a pivot 26, in turnmounted on a substrate 12. The cantilevered beam 16 may be coupled to anextension 18 secured to the free end of the beam 16. An electricalcontact 22 is positioned on the underside of the free end of the beam16.

[0016] The cantilevered beam 16 is electrically drawn towards thesubstrate 12 by the attractive force supplied from an actuator 14 a. Atthe same time, the extension 18 can be drawn towards the substrate 12 byan actuator 14 b. When the cantilevered beam 16 approaches the substrate12 sufficiently, an electrical contact is made between the contact 22 onthe beam 16 and a contact pad 24 on the substrate 12.

[0017] By application of a voltage to both actuators 14 a and 14 b, theamount of force that must be applied to the beam 16 may be decreased. Asa result, the amplitude of the actuating voltage may be reduced.

[0018] At the same time, the beam 16 may be made relatively stiffbecause its stiffness is not a problem in terms of actuating force. Inother words, a stiffer beam 16 may be utilized that reacts more quicklyin higher frequency switching applications. At the same time, the beam16 has lower actuation force, given the stiffness of the beam 16, due tothe fact that the extension 18 and the actuator 14 b enable lowervoltages to be utilized to close the switch 10.

[0019] In some embodiments, a relatively thin dielectric layer 20 may bepositioned over the actuator 14 b. As shown in FIG. 2A, the extension 18may contact the dielectric layer 20. If the dielectric layer 20 were notpresent, the protrusion of the contact 22 might interfere with properoperation of the extension 18 in some embodiments.

[0020] As shown in FIG. 2A, upon application of a voltage to theactuator pad 14 b, the extension 18, which may be more flexible than thebeam 16, is deflected toward the actuator 14 b and, particularly, itsfree end is deflected to contact the dielectric layer 20. Thus, theactuation voltage may be determined by the relatively more compliantextension 18. At a voltage that is lower than what would be needed topull down the stiff cantilevered beam 16, the more compliant extension18 is bent beyond stability.

[0021] Because the dielectric layer 20 is thin and the electrostaticforce is proportional to the inverse of the gap, the thinner extension18 quickly closes, as shown in FIG. 2B. At the same time, the thickercantilevered beam 16 is pulled down by the thinner extension 18, asshown in FIG. 2C. As a result, lower actuation voltages may be used withhigher contact forces.

[0022] The release of the closed switch 10 begins, as shown in FIG. 3A,when the actuation voltage is turned off. Since the beam 16 is morestiff than the extension 18, it reacts more quickly than the extension18 and overcomes any possible stiction. The beam 16 immediately movesoff of the contact pad 24 when the actuation force is removed from thepad 14 a. The thinner, more compliant, extension 18 is pulled away fromthe actuator 14 b by the stiffer cantilevered beam 16, as shown in FIG.3B. Eventually the extension 18 pulls away from the dielectric layer 20,as shown in FIG. 3C, resulting in complete separation and completeopening of the switch 10.

[0023] Referring to FIG. 4, the switch 10 is a broad side switch inaccordance with one embodiment of the present invention. In this case,the electrical contacts are made to a pair of laterally extending signallines representing by separate, aligned contact pads 24. In such a case,the beam 16 may have a pair of contacts 22 which separately make contactto each pad 24, each of which extend away from the beam 16 in adirection transverse to the length of the beam 16 in one embodiment.

[0024] Referring to FIG. 5, the switch 10 may also be implemented as anin-line switch, as another example. The beam 16 itself may be part ofthe signal line. In this case, extensions 18 may extend laterallyoutwardly from the free end of the beam 16 in a direction transverse tothe length of the beam 16, as shown in FIG. 6.

[0025] Thus, as shown in FIG. 6, the wing-like extensions 18 extendtransversely away from the cantilevered beam 16. The dielectric layer 20may be positioned beneath each extension 18. The actuator 14 b may belocated underneath the layer 20. At the same time, the signal line orcontact pad 24 may extend in-line, along the length of the cantileveredbeam 16 in one embodiment of the present invention. A contact 22 on theunderside of the cantilevered beam 16 may make electrical contact withthe pad 24.

[0026] While the present invention has been described with respect to alimited number of embodiments, those skilled in the art will appreciatenumerous modifications and variations therefrom. It is intended that theappended claims cover all such modifications and variations as fallwithin the true spirit and scope of this present invention.

What is claimed is:
 1. A method comprising: forming amicroelectromechanical system with a cantilevered beam; and forming anextension on said cantilevered beam that is more flexible than saidbeam.
 2. The method of claim 1 including forming said cantilevered beamover a substrate and providing an actuator in said substrate to attractsaid beam to said substrate.
 3. The method of claim 2 includingproviding an actuator in said substrate to attract said extensiontowards said substrate.
 4. The method of claim 3 including forming adielectric between said actuator and said extension.
 5. The method ofclaim 1 including providing an electrical contact on the lower surfaceof said cantilevered beam near its free end.
 6. The method of claim 1including providing a contact pad on said substrate.
 7. The method ofclaim 1 including closing said switch by first deflecting said extensionand then deflecting said cantilevered beam.
 8. The method of claim 1including opening said switch by first moving said cantilevered beam andthen moving said extension from said substrate.
 9. The method of claim 1including forming a broad side switch.
 10. The method of claim 1including forming an inline switch.
 11. A microelectromechanical systemcomprising: a substrate; a cantilevered beam formed over said substrate;and an extension formed on said cantilevered beam, said extension beingmore flexible than said beam.
 12. The system of claim 11 wherein saidbeam includes a free end and said extension extends from said free endof said beam.
 13. The system of claim 12 including an electrical contacton the free end of said beam.
 14. The system of claim 13 wherein saidcontact contacts a contact pad on said substrate, said substrate padbeing generally aligned with the length of said beam.
 15. The system ofclaim 11 including a pair of pads and a pair of contacts on said beam,said pads being contacted by said contacts on said beam, each of saidpads extending away from said beam in a direction transverse to thelength of said beam.
 16. The system of claim 11 including an actuatorfor said beam and an actuator for said extension.
 17. The system ofclaim 16 wherein said actuators are separate.
 18. The system of claim 11including a first actuator aligned with said cantilevered beam and asecond actuator aligned with said extension, said cantilevered beambeing movable towards and away from said substrate, said beam furtherincluding a contact which contacts a contact pad on said substrate, saidextension contacting said substrate before said cantilevered beam. 19.The system of claim 18 wherein said cantilevered beam moves away fromsaid substrate before said extension.
 20. The system of claim 11including an actuator for said extension, said actuator formed in saidsubstrate, said actuator being covered by a dielectric material.
 21. Amicroelectromechanical system switch comprising: a substrate; a firstmovable element mounted on said substrate; a second movable elementcoupled to said first movable element, said second movable element beingmore flexible than said first movable element; a first electricalcontact on one of said first and second movable elements; a secondelectrical contact on said substrate; and said first movable element andsaid second movable element movable towards and away from said substrateto make or break an electrical connection between said second electricalcontact on said substrate and said first electrical contact on one ofsaid first and second movable elements.
 22. The system of claim 21wherein said first movable element is a cantilevered beam.
 23. Thesystem of claim 22 wherein said second movable element is a cantileveredbeam.
 24. The system of claim 23 wherein said first movable element iscoupled on its free end to said second movable element.
 25. The systemof claim 24 wherein said first electrical contact is positioned near thefree end of said first cantilevered beam.
 26. The system of claim 21wherein said first movable element has a pair of opposed ends, saidfirst movable element supported only on one of its ends.
 27. The systemof claim 21 including a first actuator for said first movable elementand a second actuator for said second movable element, said first andsecond actuators being positioned on said substrate.
 28. The system ofclaim 27 wherein said first and second actuators are electrostaticactuators and are independent from one another.